..................... is the phenomenon by which the synthesis of a set of enzymes leading to a product is shut down, when the product is provided from outside.

Explanation

The phenomenon described in the question is known as **repression**. Here is a step-by-step explanation of the concept:

### Step-by-Step Solution:

1. **Understanding Enzyme Synthesis**: Enzymes are proteins that facilitate biochemical reactions in the body. They are synthesized based on the genetic information encoded in DNA.

2. **Role of Genes**: Genes are segments of DNA that provide the instructions for synthesizing specific proteins, including enzymes. When a gene is expressed, it leads to the production of mRNA, which is then translated into a protein.

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